Power press



NOV. 26, 1946. I KANN 2,411,543 v POWER PRESS Fil ed March 14, 1942 5. SheetsSheet 1 I INVENTOR. EDUARD KAN N AGENT.

Nov; 26, 1946. E.- KANN 2,411,543

POWER PRESS Filed March 14, 1942 5 Sheets-Sheet 2 42 I I I EDUARD KANN BY W07 AGENT N v. 26, 19 6- E. KANN 2,411,543

' POWER PRESS v Filed March 14, 1942 5 Sheets-$heet 3 Patented Nov. 26, 1 946 POWER PRESS Eduard Kann, Summit, N. J., now by judicial change of name to Edward Cann Application March 14,1942, SerialNo. 434,708

My invention relates to power presses and more particularly to the clutch mechanisms and control mechanisms of such presses.

The clutch mechanisms employed in power presses of either the crank or excentric type are one of the most important parts of the presses and it has always been difiicult to provide a mechanism which operates satisfactorily and at the same time is safe. This difficulty is due mainly to the fact that the crankshaft, which is normally stationary, must be coupled almost instantaneously to the flywheel which revolves continuously at a speed of from 50 to 500 R. P. M.

Although, it is generally considered a faulty mechanical principle to use a jaw clutch in applications such as this, it has been common practice to provide power presses with a jaw or similar clutch such as a bolt clutch or a revolving key clutch. However, these positive-acting and hammering clutches have always given, and are still giving, considerable trouble when used in power presses and are the cause of thousands of accidents resulting from so-called frepeat strokes, i. e. unexpected engagements due to defects in the clutch mechanism. Apparently press-builders have adhered to this faulty principle and have used such clutches only because of the necessity of obtaining an instantaneous engagement. More particularly, the time between the moment of tripping the clutch and the moment at which full torque is required must be less than the time of one half revolution.

Friction clutches of the, usual design are unsatisfactory for presses which operate at speeds of 50 R. P. M. and above, and in practice only slow-running heavy presses have been equipped with a friction clutch. Although friction clutches are used to some extent in fast-running presses, they have proven unsatisfactory because the powerful friction clutches necessary for this purpose are generally too heavy to operate properly. To

overcome this difficulty it has been proposed to use compressed air, hydraulic operation or servo mechanisms, some of which use screwing or weds ing members by which more force is applied to the friction members when the resistance met by the machine increases. However, with such mechanisms an indefinite torque may b applied, and this torque may exceed the torque for which the machine is designed.

The main object of my invention is to overcome the above difficulties and to provide a power press which has a friction clutch mechanism which operates satisfactorily under all conditions.

A further object is .to provide, a power press 11 Claims. (01. 19233) clutch mechanism which islsafe and will not cause accidents dueto repeat strokes,

A still further object is to provide a clutch control mechanism whereby the press can be readily used'for either single stroke operation or for continuous operation.

Another object is to provide a clutch mechani'sm which is operated almost entirely by the power supplied to the press and can be con trolled with little manual effort. I

A still further object is to provide a control mechanism whichcan be used on various types of presses and which is safe in operation and requires little force to operate.

Further objects and advantages of my invention will appear as the description progresses.

In accordance with the invention I use a friction clutch, preferably of the servo type, and control the same by a toggle mechanism which, when in a substantially dead center or inoperative position, holds the clutch in its disengaged position against the action of a spring which tends to place the clutch in its engaged position.

In accordance with the invention the clutch is tripped by moving the toggle into such a position that the clutch will be almost instantaneously engaged by the action of the spring. For this purpose I provide control means comprising a so-called box-rod which is adapted to hold the toggle in its closed position and to move the same into its operative position.

To disengage the clutch I provide a cam member which is adapted to be placed in the path of the toggle, which is rotated when the clutch is engaged, so as to close the toggle and place the same under the control of the box-rod. I

In one embodiment of the invention I provide a lever mechanism to either actuate the box-rod for single stroke operation or to move the cam member out of the path of the toggle for repeat stroke operation. I

In single stroke operation it is necessary that the box-rod bereturned to the position in which it receives the toggle from the cam member and for this purpose the box-rod is connected to a cam secured to the shaft of the press.

The clutch is preferably in the form of an internally-expanding friction brake which is forced into its engaged position by a spring and is held in its disengaged position by the toggle mechnism, When the clutch revolves during a stroke the toggle engages the cam member which places the toggle in its locked position in which it is held by the box-rod. When it is desired to operate the press thebox-rod is moved so as to release the toggle and permit the spring to exwith the parts in another position and with some of the parts omitted,

Fig. 4 is a side view of a control mechanism according to the invention,

Fig. 5 is a side view on a slightly reduced scale of the control mechanism of Fig. 4 with the parts in another position,

Fig. 6 is a, front view of a friction clutch according to another embodiment of the invention, and

Figs. 7, 8 and 9 are side views with the parts in different positions of a toggle control mechanism.

The power press shown in Fig. 1 has a frame I which. maybe of the usual design. Rotatably mounted upon the upper portion of the frame by suitablebearings is a driven member in the form of a crank shaft 2 to which is rotatably secured a ram 3 guided so as to reciprocate in a vertical direction. As this portion of the press may be of any of the usual designs, further description or more detailed illustrations of the same is believed to be unnecessary.

Mounted on the extending end of the crank shaft 2 by means of roller bearings 4 is a driving member in the form of a flywheel 5, which may be driven in the usual manner by a belt (not. shown). Flywheel 4 is provided with a cylindrical rib 6 whosev inner surface forms part of the clutch mechanism according to the invention.

In accordance with the invention the press is provided with a friction clutch for connecting the shaft 2 to the flywheel 5. As shown more clearly in Figures 2 and 3, the clutch comprises two friction shoes 9 and I which may be provided on their outer surfaces with any of the well-known friction linings. As shown in Fig. 2 the friction shoe 9 has its upper end rotatably mounted on a stud II secured to a spider l which is fixedly secured to the end of shaft 2 by a key 8. Similarly friction shoe II] has its upper end rotatably mounted on a stud I2 secured to the spider I. The friction shoe 9 has its lower end pivotedat I3 to one endof a link I5 which has its other end connected to one end i of a link I6 whose other end is pivoted at I4 to the lower end of the friction shoe II]. The links I5 and I9 are rotatably secured together at their other ends by a pin I! which carries a roller I8 later to be referred to. The lower ends of friction shoes 9 and ID are forced apart by a compression spring I9.

It will be noted that links I5 and I6 and spring I9 form a toggle mechanism, which when inits inoperative or locked position shown in Fig. 2, holds the friction shoes 9 and I 0 in their open or disengaged position. I

It will be noted that link I6 engages a stop 6| secured to the friction shoe l0 and that in this position the connecting point of links I5 and I6 is slightly past dead center whereby the spring I9 holds the links in position.

If the roller I8 is given a small displacement downward, the spring I9 will force the friction shoes 9 and I0 against the innersurface of rib B to thereby couple the driving pulley 5 to the shaft 2 and at the same time will move links I5 and I 6 into the position shown in Fig. 3. Because of this toggle arrangement only a very small force is usually required to actuate the clutch or to hold the same .in its disengaged position. Furthermore, the clutch is engaged with a predetermined pressure which depends upon the compression of spring I9. Due to the use of the toggle mechanism the full pressure of spring 4 I9 will be effective almost instantaneously. Thus, the friction between the shoes 9 and Ill and the inner surface of the ribB will reach its maximum value at once and there will be no gradually increasing friction as in other types of clutches.

The control mechanism for controlling the friction clutch comprises a cam member pivotally mounted at 2| (Figures 2 and 3) to a bracket 22 secured to the frame I (Fig. 1). As shown in Figs. 1 and 2 the member 20 has an extension 23 provided with a curved surface 24 adapted to be engaged by the roller I8 when the toggle mechanism comprising links I5 and I6 is in its open position shown in Fig. 3. Cam member 29 is prevented from rotating clockwise from the position shown inFigs. 2 and 3 by a stationary pin I03 which extends through a curved slot I92 in member 20. Pin I03 has one end secured to the frame I (see Fig. l).

Pivotally secured at one end to a stud 25 fixedly secured to frame I (see Figs. 1 and 2) is a lever 26 provided at its central part with a roller 2! adapted to be engaged by a cam 28 fixedly secured to shaft 2. Cam 28 is adapted to act upon roller 21 so as to lift lever 26 into the position shown in Fig. 2 during each revolution of shaft 2. A spiral spring IIlIl (see Fig. 2) mounted on stud 25 and having one end fixed to the stud and its other endsecured to the lever 26 prevents rod 29 from falling from the position shown in Figure 2. Although the spring I00 may lift the lever 26, the cam 28 provides a positive lifting of this lever especially during the rapid operation of the press. Pivoted to the other end of lever 26 at 93 is a so-called box-rod 29 provided near its central portion with a groove 30 adapted to receive roller I8 as it leaves the surface 24 of extension 23. A link 3| has one end pivoted. at 3.2 to the box-rod 29 and has its other end pivotally mounted on a pin 33 which is fixedly secured to frame I. Link 3! serves'to pull the lower end of rod 29 to the right when the rod is moved downward in a manner later to be described.

As shown more clearly in Fig. 2 the lower end of rod 9 is provided with a catch 34 which is held in the position shown against a stop 9I by a tension spring 35 having one end secured to rod 29 and its other end secured to an extension of the catch 34. Pivotally mounted at one end to a pivot 36 secured to frame I is a rod 31 whose other end is adapted to be engaged by the catch 34. Rod 31 is held in the position shown in Fig. 2 by a tension spring 38 having its upper end secured to a stud fixed toframe I and a stop 39 also fixed to frame I. Rod 31 is adapted to be rotated in a clockwise direction by a foot pedal 40 pivoted at 4| and connected to member 31 by a link 42.

The operation of the press will be described with reference to Figs. 2 and 3. In Fig. 2 the clutch is held in its disengaged position because the roller I8 is. held within the groove 30, and the flywheel 5 is being continuously rotated in the direction indicated by arrow a. When it is desired to trip the press, the foot pedal 40 is depressed to thereby pull the box-rod 29 downward. Rod 2'9 pulls the roller I8 downward to thereby unlock the toggle formed by links I5 and lB and during its downward movement rod 29 is drawn to the right by the member 3I. As a result the roller I8 will leave groove 30 and will be moved into the position shown in Fig. 3 by the action of spring I9. The spring I9 will thus be free to force the friction shoes 9 and I9 into contact with the inner surface of rib B. As a result the shaft 2 will be immediately connected to the flywheel and the press will start its stroke.

From the above it will be noted that in Fig. 2 the clutch is securedly held in its open position without the exertion of any appreciable force by the control mechanism. .-In*addition,it will be noted that very little force need be exerted by the control mechanismin order to engage the clutch. More particularly; it is only necessary to trip the toggle mechanism by moving the roller l8 out of the position shown .in Fig. 2.

During the stroke the toggle l5--I6 rotates.

while the links l5 and I6 and roller l8 remain in the relative positions shown in Fig. 3. The cam 28 also revolves to return the rod 29 to the position shown in Fig. 2. Near the endof the stroke the roller [8 strikes surface 24 and is guided by this surface into the groove 39. During this action the links ,9 and I9 are moved into the position shown in Fig. 2, whereby the friction shoes 9 and ID are disengaged from the surface of rib 6. The apparatus is thus returned to the position shown in Fig. 2 and a second stroke can be effected by depressing the foot pedal 49.

It should be noted that the connection between the driving pulley 5 and the crankshaft 2 is not a solid mechanical connection, but is a friction coupling which will slip if an obstruction of any kind occurs. This slipping action allows one to solve the overload relief problem in a simple and reliable manner. An accurately calculated and predetermined torque will be transmitted if the spring I9 is correctly calculated and adjusted. An arrangement for adjusting the compression of spring l9 as well as one for adjusting shoes 9 and [9 to take up the wear, of the lining should be incorporated in the clutch. However, as both of these may be of the usual design it is believed that a detailed description or illustration of the same is unnecessary.

It should be noted that to prevent injury to the operator b y the positive lifting of the boxrod 29 by cam 28, the foot pedal 49 is not directly connected to this box-rod. On the contrary the actuating mechanism 49-42-31 is automatically disengaged from the box-rod 29 and is connected thereto only when the rod 29 is in the position shown in Fig. 2, i.'e. after the operator has removed his foot from pedal 49.

Figures 4 and 5 illustrate a mechanism which can operate the press for either single or repeat strokes and in these figures the parts shown in Figs. 1 to- 3 are indicated by the same reference numerals. As shown in Fig. 4 the cam member 29 is rotatably secured at 2| to the bracket 22 and is held in the position shown by a tension spring 59 having one end fixed at 5|. Pivoted to member 29 at 52 is an arm 53 provided with a protuberance 54. The free end of arm 53 rests upon an eccentric member 94 which is rotatable about a fixed pivot 55 and; which serves to place the apparatus in condition for either a single stroke or a continuous stroke operation. A bell crank lever 56 isrotatably mounted on a fixed pivot 5'! and is provided with a pin 58 engaging the protuberance 54. The other end of crank 56 I engages the catch 34 and has connected to it the spring 38 and members 42 and 49 of Fig. 2.

by a tension spring 64 having one end fixed at BI and is adapted to be rotated clockwise by a foot pedal 62 connected thereto by a rod 63.

7 as described above in connection with Figs. 2 and Mounted on a fixed point 59 is a catch 99 Y which serves to holdthe cam member 29 in the "repeat-stroke position shown in Fig. 5. The

catch 89 is held in the position shown in Fig. 4 i

3 to thereby engage the clutch. However, at the same time pin. 58, moves arm 53 to the right to thereby swing the cam member 29 into the repeat stroke position shown in Fig. 5 in which this member is held by the catch 69. Thus, the cam surface 24 of the member 29 is placed out of the circular path of the roller 3' and the clutch will not be disengaged. After the desired number of strokes have been made the clutch may be disengaged by pressing pedal 62 to thereby release the catch 69.

When it is desired to use the press for single stroke operation, the eccentric 94 is rotated throughi180 to thereby lift the end of 'arm 53 and remove the protuberance 54 from the path of pin 58. In this case the apparatus. operates the same as described above in connection with Figs. 2 and 3.

It Will be noted that also in Figs. 4 and 5 the box-rod does not engage the lever 56 when the foot pedal 49 is being held down and thisprevents injury to the operator.

The clutch illustrated in Fig.6 is similar to that of Figs. 1, 2 and 3 and has similar parts indicated by the same reference numerals. However, in Fig. 6, the friction shoes 9 and [9 have their free ends connected by links 66, 61 and 68 and the roller [8 is secured touone end of a lever 69 whose other end is fixedly secured to the 1 link 68.

If the tripping of the clutch requires a large amount of force, for instance'if the spring [9 of Fig. 2 is very strong, I prefer to use a servotrigge-r tripping mechanism of the type illustrated in Figs. '7, 8 and. 9. This mechanism, which can be used to trip other types of presses, can be directly connected to the box-rod 29 of Fig. 2 and in Figures 7, 8 and 9 the reference numeral 19 indicates an extension of the bean rod 29. It should be noted that the mechanism of Figs. '7, 8 and 9 replaces the tripping mechanism 34-31-49-42 of Fig. 2.

The mechanism of Figs. 7, 8 and 9 comprises a base 12 upon one end of which is pivoted a foot-operated bell crank lever 13 held in the position shown in Fig. '7 by a tension spring 14 and provided at its upper end with a latch 15 held against a stop 'll by a tension spring 16. Pivoted to base 12 at 19 is a link 19 provided at its upper end with a fiat surface 89 and. an offset extension 9| provided with a pin 82. Pivoted at one end to the member 19 is a link 83 having a flat lower surface'e'ngaging the fiat surface 89.

The lower end of the link 93 has a small slot 84 into which the pin 82 fits and a tension spring 85 connected between link 1'9 and the base 12 hold the linkage in the position shown.

In the position shown in Fig. 7 the box-rod 29 is in the position shown in Fig. 2 and when it is desired to trip the press it is only necessary to exert a slight downward pressure on the foot pedal '53 to'thereby pull the toggle mechanism 19-8801? dead center. The spring 85. continues the action to place, the toggle mechanism in the position shown in Fig. 8 in. which the box-rod 29 assumes the position shown in Fig; 3. The

spring .85 should have sufficient tension toensure 7 that the box-rod and roller i8 will be pulled downward under all conditions.

When the press. makes a stroke, the box-rod 29 is lifted by cam 28, as described in connection with Figs. 1, 2 and 3, with the result that the linkage IS-83 is first lifted into the position shown in Fig. 9 and is then slightly lowered so that the lower surface link 83 rests upon the flat surface 80 (see Fig. 7)

It will-be noted that the resetting of the tripping mechanism, and the stretching of spring 85 is effected by the press itself and that only a slight manual effort is required to trip the press. In addition there is no danger of injury to the operator, because the pin 82 will not engage the latch when the crank 13 is held down by the operators foot.

It will be noted that in my press as the pressure on the friction surfaces of the clutch is not positive but is applied by a spring, a predetermined pressure resulting in a predetermined torque is easily obtained. In addition release of the clutch shoes is positive and is obtained by the motion and the driving power of the press. Furthermore, operation of the clutch is very light as a result of a very simple servo-action, engaging and disengaging are both practically instantaneous, and there is very little slipping during the engagement.

Some presses give difficulties when it is necessary to rotate the crankshaftbackward by hand. This is sometimes required by the user but often forgotten by the builder of the press. In the design described above reverse motion is quite feasible. Once the clutch is engaged (and this can be done by moving the box-rod) the flywheel may be turned back and the crankshaft follows. No damage is done to the mechanism and when roller l8 in its swung-out position hits the cam member from beneath, it forces the cam member outward and passes by. For this purpose the lower end of the cam is given a suitable shape.

With some of the existing positive-acting clutches damage can be done by overrunning. This is the case if the crankshaft temporarily runs faster than the flywheel due to the weight of the ram during downward stroke or to the back pressure of the die cushion during upward strokes. If this is not prevented by a pawl the overrunning may cause severe damage to the clutch mechanism. With the friction clutch according to my invention .and as described above overrunning causes no difficulty because the clutch couples the flywheel to the crankshaft equally well in either direction.

My press may be provided with interlocking guards which not only interlock the actuating mechanism, but also the crankshaft (see also Proceedings National Safety Congress, London 1939 and American Machinist, September 18, 194-0) This interlocking of the crankshaft makes an overload relief necessary. If the latter is added as an extra feature to a press having the usual clutch mechanism, it would make the application of this safety device too expensive. The in-- stantaneous friction clutch described above facilitates the application of safety devices, because it obviates the old positive clutch and at the same time acts as an overload relief,

Although I have described my invention with reference to specific constructions I do not desire tobe limited thereto because constructional variations will readily appear to one skilled in thisart.

and a driven. member, a; clutch mechanism for connecting the driven member to the driving member and comprising a friction shoe having an engaged. position in. which it engages said driving member and a disengaged position, a resilient member acting upon said shoe to force the same into its engaged position, and means to hold said friction shoe in its disengaged position against the action of said resilient member, said 1atter means including a toggle mechanism connected tosaid friction shoe and rotatable therewith and being in a substantially-locked position when the shoe is in the disengaged position, and means to direct said toggle fromits engaged position into its substantially-locked position during rotation of the clutch mechanism, said latter means including a member adapted to be placed in the path of said toggle during the rotation of the friction shoe and toggle with the driving member.

2. In a power press having a driving member and a driven member, a clutch mechanism for connecting the driven member to the driving member and comprising a friction shoe having an engaged position in which it engages said driving member and a disengaged position, a resilient member acting upon said shoe to force the same into its engaged position, and means to hold said friction shoe in its disengaged position against the action of said resilient member, said latter means including a toggle mechanism connected to said friction shoe and rotatable therewith and being in a substantially-locked position when the shoe is in the disengaged position, means to hold said toggle mechanism in its substantially-locked position, and means to move said toggle mecha nism into its substantially-locked position and to direct the mechanism while in said position into said holding means during rotation of the clutch mechanism.

3. In a power press having a driving member and adriven member, a clutch mechanism for connecting the driven member to the driving member and comprising an internally-expanding friction shoe adapted to engage said driving member, a resilient member arranged to force said shoe into its engaged position, and. means to hold said friction shoe in its disengaged position against the action of said resilient member including a toggle mechanism connected to said friction shoe and being in a substantially-locked position when said shoe is disengaged, a box-rod to receive said toggle and hold the same in a substantially-locked position, and a cam-like member to direct the toggle from its engaged position into said box-rod during rotation of the clutch mechanism.

4. In a power press having a driving member and a driven member, a clutch mechanism for connecting the driven member to the driving member and comprising a friction hoe having an engaged position in which it engages said driving member and a disengaged position, a resilient member acting upon said shoe to force the same into its engaged position, and means to hold said friction shoe in its disengaged position against the action of said resilient member, said latter means including a toggle mechanism connected to said friction shoe and being in a substantiallylocked position when the shoe is in the disengaged position, means to direct said toggle mechanism into a substantially-locked position during rotation of the clutch mechanism, and means to move said toggle mechanism out of its; substantiallylocked position to thereby trip the press.

5. In a power press having a driving member and a driven member, a clutch mechanism for connecting the driven member to the driving member and comprising a friction shoe adapted to engage said driving member, a resilient member arranged to force said shoe into its engaged position, and means to hold said friction shoe in its disengaged position against the action of said resilient member including a toggle mechanism connected to said friction shoe and being in a substantially-locked position when said shoe is disengaged, said toggle mechanism moving in a circular path when said clutch mechanism is engaged, a cam-like member to direct the toggle from its engaged position into a substantiallylocked position during rotation of the clutch mechanism, and means to place said cam-like member into and out of the path of said toggle mechanism.

6. In a power press having a driving member and a driven member, a clutch mechanism for connecting the driven member to the driving member and comprising a friction shoe having an engaged position in which it engages said driving member and a disengaged position, a resilient member acting upon said shoe to force the same into its engaged position, and means to hold said friction shoe in its disengagedposition against the action of said resilient member, said latter means including a toggle mechanism connected to said friction shoe and being in a substantiallylocked position when the shoe is in the disengaged position, a box-rod for holding said toggle mechanism in its substantially-locked position and to remove the same therefrom when the press is tripped, a cam-like member to direct said toggle from its engaged position into its substantiallylocked position during rotation of the clutch mechanism, and means actuated by said driven member to place said box-rod into a position in which it receives the toggle mechanism from the cam-like member.

'7. In a power press having a driving member and a driven member, a clutch mechanism for connecting the driven member to the driving member and comprising a friction shoe having an engaged position in which it engages said driving member and a disengaged position, a resilient member acting upon said shoe to force the same tion in which said toggle is held in its substantially-locked position and a second position in which the toggle mechanism is free from the member, means actuated by the driven member to return the box-rod to its first-mentioned position, and means to direct said toggle mechanism during rotation of the clutch mechanism into said box-rod.

8. In a power press having a driving member and a driven member, a clutch mechanism for connecting the driven member to th driving member and comprising a friction shoe adapted to engage said driving member, a resilient member arranged to force said shoe into its engaged position, and means to hold said friction shoe in its disengaged position against the action of said resilient member including a toggle mechanism connected to said friction shoe and being 10 in a substantially-locked position when said shoe is disengaged, a box-rod to hold the toggle mechanism in and remove the same from a substantialiy-locked position, a cam-like member to direct the toggle into said box-rod during rotation of the clutch mechanism, and a second toggle mechanism for actuating said box-rod.

9. In a power press having a rotatable driving member and a rotatable driven member, a clutch mechanism for connecting the driven member to the driving member, said mechanism comprising a friction shoe having an engaged position in which it engages the driving member and a disengaged position, a resilient member acting upon said shoe to force the same into its engaged position, and a toggle mechanism connected to said friction shoe and being in a substantially-locked position when the shoe is in its disengaged position, said toggle including two links and a pivot connecting said links, said pivot passing along a circular ath during rotation of said clutch mechanism, and means for controlling said clutch mechanism, said latter means comprising a cam-like member adapted to be placed in the path of said pivot so as to place the toggle mechanism in its substantially-locked position, a box-rod having a position in' which it receives the pivot from said cam-like member and a second position out of the path of the pivot, means to move said box-rod from the first position to the second position, and means actuated by the driven member to return said box-rod to its first position during rotation of the clutch mechanism.

10. In a ower press having a rotatable driving member and a rotatable driven member, a clutch mechanism for connecting the driven member to the driving member, said mechanism comprising a pivot secured to said driven member and rotatable therewith, a friction shoe having one end supported by said pivot, a spring arranged to force said friction shoe into engagement with said driving member, a toggle mechanism connected to said friction shoe to hold the same against the action of said spring, said toggle mechanism being rotatable with said friction shoe and being in a substantially-locked position when said friction shoe is disengaged, and means adapted to be placed in the rotational path of said toggle to direct the same into its substantially-locked position.

11. In a power press having a rotatable driving member and a rotatable driven member, a clutch mechanism for connecting the driven member to the driving member, said mechanism comprising two pivots secured to said driven member and rotatable therewith, two friction shoes each rotatably supported at one end on one of said pivots, said shoe having engaged positions inwhich they engage said driving member and disengaged positions, a toggle mechanism having an open position and a substantially-locked position, said toggle mechanism comprising two links each having one end connected to the end of one of said shoes, a linking member having each of its ends connected to one of the other ends of said links and a compression spring arranged to force said toggle into its open position and said shoes into their engaged positions, a member adapted to be placed into the rotational path of saidtoggle whereby said toggle during its rotation with said driven member is moved into its substantiallylocked position, and means to move said toggle from its substantially-locked position.

EDUARD KANN, 

